1. Field of the Invention
The present invention generally relates to the filtering of liquids and more specifically to the high-purity filtration of high temperature etching liquids, primarely used in the processing of semiconductor devices and requiring very high reliability at an extremely low particle count, and to the filtration of liquids in the pharmaceutical and chemical industries.
2. Description of the Prior Art
Presently available filter housing assemblies use cartridges inserted into a cylindrical housing with a twist-screwtop to tighten an O-Ring against the housing flange for generating a sealed unit with an inlet and an outlet for the liquid to be filtered. The liquid enters under pressure through the inlet into the space between the housing and the cylindrical filter cartridge and is forced radially inward through the filter. The filter surrounds a concentric cylindrical space through which the filtered liquid exits from the outlet at the bottom of the filter housing. The filter cartridge is closed off at its top and has a nose at its bottom, surrounded by O-rings, by which the cartridge is held in the bottom recess of the filter housing. Potential shortcomings of the filter housing are damage to the O-ring because of twisting, deforming and abrasive action during screw-on closure, which can contribute to leakage and a decrease in filtration efficiency. Usually the cartridge is inserted and held only at the housing bottom by two parallel O-rings around the cartridge nose. The filter cartridge may tilt as a consequence of fluid pressure action and no longer be concentric with the filter housing, causing an uneven flow through the cartridge. This action also may contribute to lower filtration efficiency and a higher particle count by uneven filtration or by bypassing of the filter as well as to lower filter cartidge life. Together with the used cartridge filter housings are often thrown away, amounting to economical and environmental waste. Where ultrapure filtration is needed, several filters, possibly with decreasing particle size, may be used, requiring several filter housings in sequence at an increased cost. Molded orifices at the top portion of the housing have been used to relieve over-pressure or for back-flushing.